Fix commit silently failing when using a long text

In Studio (reproduced on prod, nos-test and nos-dev)

Using intermediate commit mode
Make a modification
Press the commit icon
Put a long commit message
Press commit and push button

=> Commit and push silently fails, nothing shows up in the console but an error 500 happens in the server

Expected:

• If Studio can accept longer commit messages, accept them without triggering an error (best solution).
• If Studio can't accept longer commit messages, then it should display a character count (e.g. 500 / 1024 characters, updated dynamically), block longer messages than what's accepted client side and truncate the message server side if user bypasses this protection (degraded solution, to be used only if best solution is technically not possible).